The near-infrared region corresponds to an absorption spectrum range related to biological objects such as plants and animals, and the environment. Therefore, the development of a detector of near-infrared light, the detector including a light-receiving layer composed of a group III-V compound semiconductor corresponding to the near-infrared light has been actively conducted. For example, NPL 1 discloses an example of a detector that converts photo-induced charge into an output signal, the detector including a light-receiving element array in which the sensitivity is extended to a wavelength of 2.6 μm by using extended-InGaAs as a light-receiving layer and a complementary metal-oxide semiconductor (CMOS) which is a read-out circuit (ROIC: read-out IC) and is connected to the light-receiving element array. In the light-receiving element array, electrons of electron-hole pairs generated by incident light are collected in a common n-side electrode, and holes of the electron-hole pairs are read out from a p-side electrode, which is a pixel electrode, to the CMOS.
In addition, NPL 2 has reported that a pin-type photodiode including a light-receiving layer having a type-II multiquantum well structure (MQW) composed of InGaAs/GaAsSb and a p-type pixel region has a sensitivity up to a wavelength of 2.5 μm.